Protection of steel oil and/or gas well tubing



May 2,1961 B. B. MORTON ET-AL 2,982,360

PROTECTION OF STEEL OIL AND/OR GAS WELL TUBING Filed 001;. 12, 1956 FIG! FIG.2

5; BYRONBENSON MORTON RUTLEDGE ST JOHN RICE INVENTOR'S BYQLQMSQQQ ATTORNEY Unite Patent Promotion OF STEEL OIL Ann/oRcXs YWELL'IIUBING Byron B. Morton, Elizabeth, N.J.,-a.1 Rutledge st. John Rice, Houston, Tex., assignors to The International Nickel Company, Inc.', New York, N.Y., a corporation ofDelaware Filed 0ct.1 2, *1956,;,Ser. :No. 615,494

4 Claims. (Cl. ire- 242) The present invention relates to steel oil and/orgas tubing and, more particularly, to theprotection .of steel art, serious problems and diffic'ultieshave heretofore x existed with respect towthe utilization of steel oiland/or gas well tubing which, while in service, is prone to failure caused by a mechanism involving hydrogen and/ or stress.- corrosion cracking. Hydrogen cracking or embrittlement can be' generally considered a spontaneous failure of metal as the result of atomichydrogen acting within interstitial voids :in the metal, i.e.,..discontinuities in the atomic structure of the metal, in the presence of some minimum stress. Stress-corrosion cracking has been defined as including any combined effect of stress and corrosion on the behavior of metals. Either type of failure may be generically categorized as a, type of brittle failure, ,the mechanism of. which can be considered as encompassing two stages. Inthe first stage, a crack or pit is developed in the metal and is continued by high stresses -and/or corrosion until the crack or pitcrack reaches a critical length with respect to the stresses acting normal to the length thereof. In the second stage, the crack is continued beyond the critical length until failure occurs.

The problems and difficulties have become particular- .ly acute anent deep, sour oil and/or gas wells. In such wells, hydrogen is activated in a manner whenceit comes into intimate contact with thesteel tubing. The hydrogen in atomic or nascent form penetrates the voids present in the metal and subsequently, because of its native activity, forms molecular hydrogen and thus causes an expansion in the volume of hydrogen in the void. This expansion, so caused, exerts a pressure of ever increasing proportion whereby the formation and lengtheningof cracks occur until pressure-causes complete fracture. The atomic hydrogen may be activated in several ways. For example, hydrogen sulphide in the fluids of sour wells reacts with the metal tubing whereby hydrogen is liberated in atomic form and then penetrates the metal. The process is facilitated .when a poisonous catalyst is formed, e.g., ferrous sulphide. The catalyst acts in a manner to encourage entrance or permeation of released atomic hydrogen into the metal. This is to say, a source of atomic hydrogen is catalytically directed into the metal. Another example of the manner in which hydrogen is introduced into wells is through well known acidizing procedures. The acid coming into contact with the steel tubing reacts therewith with the evolution of atomic hydrogen.

Conditions for the inducement of steel tubing to stresscorrosion cracking occur in a variety of ways. For example, internal stresses in the tubing metal resulting from improper heat treatment or cold work leave the metal in a condition susceptible to stress-corrosion cracking.

Patented May 2, 1961 Pit cracking or stress-corrosion in certain metals until failure fluids, cause pitting. cracking, continues occurs.

The mechanism of failure by cracking as referred to hereinabove is particularly pronounced, peculiarly enough, in steel tubing of high mechanical strength, e.g., steels having yield strengths of 80,000 p.s.i. (pounds per square inch) and up, and even more so in cold-worked high strength steels. With respect to hydrogen cracking particularly, experience has indicated that the minimum stress involved, in cracking as referred to hereinabove, apparently varies with the overall strength of the metal, the higher the strength of the metal the lower the minimum'of residual stress to bring about hydrogen cracking. Such high strength steels are generally used in commerical practice and are considered necessary for the purpose of resisting or counter-acting the effect of high tensile stresses, including both external and internal stresses, acting upon or within the metal. External stresses are generally the natural result of the use to which thesteel tubing is subjected during service whereas internal stresses primarily result from cold-working or other operations to which the steel is subjected prior to or in'use.

Endeavors directed to the use of low strength steels, e.g., yield strength of about 40,000 to 50,000 p.s.i., have not been entirely satisfactory. Such low strength steel tubing is somewhat susceptible to hydrogen and stresscorrosion cracking and there is a significant and undesirable sacrifice in mechanical strength, particularly in wells where high pressures and temperatures are encountered. Moreover, such steels are susceptible to formation of blisters which by rupturing can destroy portions or segments of the tube wall. It also has been proposed to subject both high strength and low strength steels to heatjtreatment to stress relieve the same, i.e., reduce internal stress caused by cold working. It is considered that such treatment involving relieving internal stress,

substantially reduces the number or size of the voids in the metal. However, it has been found that quenching processes employed after heat treatment set up a degree of internalstress. Moreover, it has been found generally necessary in practice that since the tubing must be straight in order to meet drift diameter requirements, cold-working procedures must be employed at various portions thereof to accomplish the same. Thus, additional internal stresses are set up and the voids in the metal are ever present and become larger at least with'respect to size. Furthermore, improper heat treatments can, as mentioned hereinbefore, be conducive to stress-corrosion cracking.

It has also been proposed heretofore to use plastic liners in steel oil well tubing for the protection thereof but'it has been found that plastic liners soften at well temperatures, e.g., 230 F. to 250 F., to such a detrimental degree that they pull loose and ball up even to the extent of stopping fluid flow. Some artisans have expressed the view that when voids occur in plastic liners the steel tubing cracks more readily than if the steel tubing were left completely exposed.

It might be well said that the problem is intensified and magnified in deep, sour wells where extremely high pressures and high temperatures, e.g., 15,000 p.s.i and about 350 F. prevail. Although many attempts were made to overcome the foregoing difficulties and other disadvantages, none, as far as we are aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that hydrogen and stresscorrosion cracking in steel tubing and particularly oil and/or gas well cold-worked steel tubing of high mechanical strength can be substantially minimized or re duced to a negligible extent by the use of special metal liners capable of protecting the steel from atomic hydrogen.

It is an object of the present invention to protect steel tubing from. hydrogen and/or stress-corrosion cracking.

Another object of the invention is to prevent failure of steel oil and/or gas well tubing in deep, sour, condensate wells caused by hydrogen and/ or stress-corrosion cracking.

The invention also contemplates providing a metal liner in combination with steel oil and/ or gas well tubing such that the steel tubing will not be subject to hydrogen and stress-corrosion cracking and will therefore be rendered capable of exhibiting a longer service life than when no such liner is used.

It is a further object of the invention to provide a metal liner capable of rendering atomic hydrogen into a form inert to steel oil and/ or gas well tubing.

The invention further contemplates protecting high strength, cold-worked steel oil and/or gas well tubing and more particularly, such steel tubing used in deep, sour wells of high pressures and temperatures from failure normally caused by hydrogen and stress-corrosion crack ing.

Other objects and advantages of the present invention will become more apparent from the description taken into conjunction with the accompanying drawing in which:

Figures 1 and 2 represent longitudinal sectional views and. Figure 3 an end view of Figure 1 showing the lined steel oil and/or gas well tubular structure provided in accordance with the present invention. In Figures 1 and 3 the interfacial zone between the tube and liner is shown on a greatly enlarged scale for purposes of illustration.

Generally speaking, the present invention contemplates protecting steel oil and/or gas tubing and particularly high strength, cold-worked oil and/or gas well tubing utilized in deep, sour Wells from failure caused or induced by hydrogen and/or stress-corrosion cracking by providing within the steel tubing, but in unbonded association therewith, a metal liner pervious to atomic hydrogen penetration, the metal liner being in mechanical contact with the steel tubing to form an interfacial zone therewith. It is important in accordance with the principles of the present invention that the outer surface of the protective liner be unbonded with respect to the inner surface of the steel tubing, i.e., the metallic liner is mechanically expanded or otherwise closely fitted to the inside diameter of the steel tubing throughout its entire length such that there is no metallic path for atomic hydrogen to pass into the steel tubing. Thus, there is a continuous void, i.e., interfacial zone, existing between the metal liner and steel tube. This feature of an interfacial zone in combination with the perviousness of the metal liner permits atomic hydrogen, which may be evolved from a reaction such as, for example, a reaction occurring between the liner and hydrogen sulfide, to preferentially reform into molecular hydrogen on the outside surface of the liner. In its molecular state hydrogen is substantially inert to the steel tubing at the temperatures within the wells. If the metal liner and steel tubing were in bonded form, e.g., clad or plated form wherein substantial diffusion occurs between the metal receiving a deposit and the deposited metal, permeation of the liner by atomic hydrogen would continue directly into the steel tubing and thus create the conditions which lead to cracking. The liner can be conveniently inserted within the steel tubing by procedures well known to those skilled in the art. For example, the liner can be expanded against the inner surface of the steel tubing using hydrostatic pressure.

In carrying the present invention into practice, it is preferred to employ metal liners containing metal from the group consisting of nickel, copper, and alloys "there- 4 of. Preferably, the nickel-copper alloys contain about 63% to nickel and about 25% to 30% copper. Small amounts of other elements including up to 2% iron, up to 2% manganese, up to 4% aluminum, up to 1% silicon and up to 0.3% carbon are contemplated within the scope of these alloys. Such liners, in addition to protecting steel tubing from hydrogen and/or stress-corrosion cracking failure, have a lower tensile modulus and higher thermal expansivity than steel and, as a result thereof, an excellent and desirable tight and permanent mechanical grip of the liner by the tubing is assured when expanded into place hydrostatically, when supporting a load in a well, and when heated by earth temperatures. Moreover, such liners are extremely corrosion-resistant to various corrosive media of well fluids, e.g., hydrogen sulfide of sour wells. It is also a preferred embodiment of the present invention where temperatures in excess of 500 F. and destructive sulfur are encountered in wells to employ metal liners pervious to atomic hydrogen and comprised of nickel-chromium-iron alloys containing nickel in amounts greater than about 50%, e.g., to chromium from about 10% to 35%, e.g., 12% to 15%, with iron being essentially the balance, e.g., 5% to 9% or 13%. Such alloys exhibit the desirable characteristic of affording substantial resistance to sulfur attack at well temperatures greater than 500 F. and are highly resistant to stress-corrosion attack normally attributable to the effect of chloride ions.

Turning to a discussion of the drawing and particularly Figure 2, there is shown a tubular structure comprised of an oil well steel tube 1 in mechanical contact, i.e., unbonded association, with a pervious metal liner 2. Reference numeral 3 indicates the interfacial zone existing between the steel tube and metal liner. This interfacial zone is shown on a greatly enlarged scale in Figures 1 and 3 for purposes of illustration. Thus, it will be understood that oil well steel tube 1 and metal liner 2 are engaged in mechanical contact such that there is formed therebetween a continuous void, i.e., an interfacial zone.

It is to be observed that the present invention provides special metal liners for the protection of steel oil and/or gas tubing from failure normally caused or induced by hydrogen and/or stress-corrosion cracking. The fact that the metal liners are in mechanical contact such that an interfacial zone is established therebetween provides a system for obviating or substantially preventing atomic hydrogen contact with the steel tubing. The establishment of an interfacial zone provides for the selective and preferential formation of molecular hydrogen on the outside surface of the metal liner. Hydrogen which heretofore contacted the steel tubing in destructive atomic or nascent state now, in accordance with the invention, contacts the tubing in harmless molecular form.

Furthermore, the invention provides for the protection of high strength, cold-worked steel oil and/or gas well tubing employed in deep, sour wells from hydrogen and/or stress-corrosion cracking. The metal liners described hereinbefore easily Withstand the high temperatures and pressures of deep wells. It is to be noted that since cold-worked steels of high strength, e.g., 80,000 psi, and containing small amounts of alloying elements, e.g., 0.75% to 1% chromium, 0.08% to 0.1% molybdenum, 0.5% to 1.25% manganese and 0.75% to 1.25 nickel, can be safely employed in oil and/or gas wells in accordance with the invention, no sacrifice in mechanical strength thereof is incurred as in the case of using low strength steels, e.g., steels having a yield strength of about 40,000 p.s.i. The voids present in the cold-workedsteel and which would have hitherto normally served as accumulators for atomic hydrogen no longer present a hazardous condition. Thus, maximum protection is coupled with maximum strength.

Moreover, the invention provides a new bi-metallic oil and/or gas well tubular structure having high overall strength and being comprised of an outer shell of coldworked and/or high strength steel and an inner shell in mechanical contact therewith and being comprised of the liner materials in accordance with the invention.

It is to be noted that the present invention is not to be confused with the more protection of steel tubing from general corrosive effects, for example, gradual corroding of metal through the formation of steel compounds which eventually become loose from the steel tubing and flake oif. Such corrosive activity which can be considered as general corrosion, although it is prevented by the present invention, is quite distinct from the problem of preventing hydrogen and/ or stress-corrosion or cracking failure.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim: i

1. As a new article of manufacture, an improved oil and/or gas well tubular. structure capable of use under relatively high pressures and temperatures in deep, sour wells and adapted to resist failure caused or induced by provide for the selective and preferential formation of molecular hydrogen on the outside surface of said liner while in service, whereby detrimental atomic hydrogen contact with said steel shell is prevented.

2. The article of manufacture as described in claim 1 wherein the metal liner is comprised of a nickel-copper alloy containing about 63% to nickel and about 25% to 30% copper.

3. As a new article of manufacture, abi-metallic oil and/ or gas welltubular structure adapted to resist failure caused or induced by hydrogen and/or stress-corrosion cracking while in service, said tubular structure being comprised of an outer shell formed of a steel possessing a yield strength of at least about 80,000 pounds per square inch and an inner metal liner pervious to atomic hydrogen penetration, said liner being comprised of an alloy containing at least 50% nickel, from about 10% to about 35% chromium, and the balance essentially iron, said shell and liner being in mechanical contact such that there existsan' interfacial zone therebetween and to thereby provide for the preferential formation of molecular hydrogen on the outside surface of said liner while in service, whereby detrimental atomic hydrogen contact with said steel tubing is prevented a 4. The article of manufacture as described in claim 3 wherein the metal liner is comprised of an alloy containing about to nickel, about 12% to 15% chromium, and the balance essentially iron.

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